It is customary to formulate herbicides as water-dispersible compositions which can be readily mixed with water and applied by means of spraying apparatus. An important class of herbicides which can be applied by this means comprises the symmetrical triazine diones, of which 1-methyl-3-cyclohexyl-6-dimethylamino-s-triazine-2,4(1H,3H)-dione is the most widely used. Formulations of this herbicide are marketed throughout the world under the trade name Velpar.RTM. weed-killing compounds (trademark of E. I. du Pont de Nemours and Company, Wilmington, Delaware).
One difficulty with many herbicide formulations is that the active ingredient has limited solubility in the water in which it is dispersed under the conditions of temperature at which the spraying is carried out. Heretofore, this has meant that the spray concentrations of many herbicides had to be limited to below its solubility limit in order to avoid crystallization within the spray apparatus and concomitant plugging of the spray nozzle. Nozzle plugging is most likely to take place when a crystal size of 150.mu. in any dimension is reached. Such plugging is of significant economic detriment for the reasons that (1) manpower time must be expended to discontinue spraying operations and remove the plugging material and (2) any area sprayed before the plugging is detected and corrected is likely to be covered inadequately. Thus, there is considerable practical need for spraying systems which have reduced plugging tendencies, which, nevertheless, can be used at relatively high concentrations.
The important symmetrical triazine dione, 1-methyl-3-cyclohexyl-6-dimethylamino-s-triazine-2,4-(1H,3H)-dione, is one of those compounds which, because of its limited solubility in water, frequently incurs plugging when used at concentrations above its solubility limit at temperatures below about 37.degree. C. (98.6.degree. F.). For this reason, liquid spray compositions containing Velpar.RTM. herbicidal compounds have been limited to concentrations of about 2-3% by weight active triazine compounds, unless they are heated to raise the solubility limit.